Evidence review
What to inspect before changing anything
Start with the delivered website and the real user journey. Record the current state so the team can distinguish an observed problem from an assumption and compare the same surface after deployment.
- 01Confirm every public route redirects to HTTPS
- 02Review max-age, includeSubDomains and preload
- 03Inventory subdomains that may not support HTTPS
Implementation
A practical improvement plan
Make the smallest coherent change that solves the observed problem. Keep normal code review, accessibility, security and product checks in the loop instead of optimizing for the scan alone.
- 01Fix certificates and HTTPS redirects first
- 02Increase max-age gradually after monitoring
- 03Add subdomain or preload directives only after domain-wide review
Verification
How to verify the result
Verification should test the intended outcome and the most likely regression. Use the production delivery path whenever headers, caching, rendering or third-party services affect the result.
- 01Inspect the final HTTPS response header
- 02Test representative subdomains and redirects
- 03Recheck certificate renewal and expiry monitoring
Common pitfall
A shortcut to avoid
Enabling includeSubDomains or preload before every subdomain is ready can make legitimate services unreachable.
Further reading
Primary guidance and references
These sources provide standards, security guidance or the interpretation framework used to keep this guide bounded. Product-specific implementation still requires review in the actual codebase.